What iron does and why your body needs it

Iron is the mineral your body uses to build hemoglobin, the protein in red blood cells that carries oxygen from your lungs to every tissue. Without enough iron, your red blood cells can't carry oxygen efficiently, which is why iron deficiency causes fatigue, shortness of breath, and difficulty concentrating. Iron also plays a role in muscle function, immune response, and energy production at the cellular level.

Your body doesn't make iron—you have to get it from food or supplements. Adult men need 8 milligrams per day; adult women aged 19 to 50 need 18 milligrams per day because menstruation causes iron loss. Women over 50 and postmenopausal women need 8 milligrams per day. Pregnant women need 27 milligrams per day because blood volume expands and the fetus draws iron for its own development.

Key Takeaways

  • Iron carries oxygen in your blood and is essential for energy, muscle function, and immune response.
  • Red meat, poultry, and fish contain heme iron, which your body absorbs more efficiently than plant-based non-heme iron.
  • Vitamin C increases iron absorption from plant sources, while tea, coffee, and calcium can reduce it.
  • Iron deficiency develops gradually and causes fatigue, weakness, and pale skin; severe deficiency can damage the heart and organs.
  • Too much iron from supplements can accumulate in organs and cause damage, so supplementation should be based on a blood test, not guesswork.

Heme iron versus non-heme iron: which sources your body absorbs better

Iron comes in two forms: heme iron and non-heme iron. Heme iron comes from animal tissue—beef, pork, poultry, and fish—and your intestines absorb 15 to 35 percent of it. Non-heme iron comes from plants, fortified grains, and supplements, and your body absorbs only 2 to 20 percent of it. This difference matters if you're vegetarian or vegan, because you need to eat more iron-rich plant foods or pair them with absorption boosters.

Good sources of heme iron include beef, chicken, turkey, salmon, and oysters. Plant sources of non-heme iron include beans, lentils, tofu, fortified cereals, dark leafy greens like spinach and kale, and pumpkin seeds. A 3-ounce serving of beef contains about 2.6 milligrams of iron; a cup of cooked lentils contains about 6.6 milligrams. Because absorption rates differ, eating a small amount of meat alongside plant iron sources can increase how much iron your body takes in overall.

How to increase iron absorption from food

Vitamin C is the most effective absorption booster. Eating vitamin C-rich foods at the same meal as iron-rich foods increases non-heme iron absorption significantly. Citrus fruits, tomatoes, bell peppers, strawberries, and broccoli all contain vitamin C. A study published in the American Journal of Clinical Nutrition found that adding 25 to 75 milligrams of vitamin C to a meal can triple non-heme iron absorption. This means pairing a spinach salad with orange slices, or beans with tomato sauce, makes a real difference.

Several foods and drinks reduce iron absorption and should be consumed at different times if you're trying to increase iron intake. Tea, coffee, and cocoa contain compounds called polyphenols that bind to iron and prevent absorption. Calcium supplements and high-calcium foods like dairy can also interfere, though the effect is smaller. If you take an iron supplement, take it on an empty stomach or with orange juice, and wait at least two hours before drinking tea or taking a calcium supplement.

Signs of iron deficiency and how it develops

Iron deficiency develops in stages. First, your body depletes its iron stores without affecting blood iron levels—this stage often has no symptoms. As deficiency progresses, blood iron drops and your body struggles to make hemoglobin. This is when symptoms appear: fatigue, weakness, pale skin, shortness of breath with normal activity, dizziness, cold hands and feet, and difficulty concentrating. Some people develop cravings for non-food items like ice, dirt, or starch—a condition called pica.

Severe iron deficiency can damage the heart, weaken the immune system, and impair cognitive development in children. A blood test measuring ferritin (stored iron) and serum iron can detect deficiency before symptoms become severe. If you have ongoing fatigue, shortness of breath, or pale skin, a doctor can order these tests. Common causes of deficiency include heavy menstrual bleeding, pregnancy, vegetarian or vegan diets without careful planning, digestive disorders that reduce absorption, and blood loss from ulcers or other bleeding.

Iron supplements: when they're needed and why more isn't better

Iron supplements are necessary when diet alone can't meet your needs—during pregnancy, after blood loss, or when absorption is impaired by digestive disease. Supplements come as ferrous sulfate, ferrous gluconate, or ferrous fumarate; ferrous forms are absorbed better than ferric forms. A typical supplement contains 25 to 65 milligrams of elemental iron per dose. Taking a supplement on an empty stomach increases absorption, though it may cause nausea; taking it with food reduces absorption but improves tolerance.

More iron is not better. Excess iron accumulates in organs like the liver, heart, and pancreas and can cause cirrhosis, heart arrhythmias, diabetes, and joint damage. This risk is especially high in people with hemochromatosis, a genetic condition that causes iron overabsorption. Iron supplements should only be taken based on a blood test showing deficiency, not on general information or symptoms alone. If you're considering supplementation, a doctor can measure your iron levels and recommend the right dose and form for your situation.

Iron needs across different life stages

Iron requirements change throughout life based on growth, menstruation, and pregnancy. Infants aged 7 to 12 months need 11 milligrams per day; children aged 1 to 3 need 7 milligrams per day; children aged 4 to 8 need 10 milligrams per day; and children aged 9 to 13 need 8 milligrams per day. Adolescent boys aged 14 to 18 need 11 milligrams per day; adolescent girls need 15 milligrams per day because menstruation begins.

Pregnant women need 27 milligrams per day, and breastfeeding women aged 19 to 50 need 9 milligrams per day. Older adults have the same needs as younger adults—8 milligrams per day for men and postmenopausal women—but may absorb iron less efficiently due to reduced stomach acid or medications. Athletes, especially female endurance athletes, may have higher needs due to iron loss through sweat and increased red blood cell turnover, though research on this is still developing.

What research shows about iron and athletic performance

Iron deficiency impairs aerobic performance because hemoglobin carries oxygen to muscles. Studies in athletes show that correcting iron deficiency improves endurance and reduces fatigue. However, taking iron supplements when iron levels are normal does not improve performance in healthy people. Some research has explored whether iron supplementation could enhance performance in non-deficient athletes, but evidence remains mixed and the risk of iron accumulation makes this approach inadvisable without medical testing.

Female endurance athletes—runners, cyclists, swimmers—have higher rates of iron deficiency than sedentary women, likely due to iron loss in sweat, foot-strike hemolysis (red blood cells breaking down from repeated impact), and sometimes inadequate dietary intake. If you're an athlete experiencing unexplained fatigue or declining performance, a blood test can determine whether iron deficiency is the cause. If it is, correcting it through diet or targeted supplementation can restore performance; if it isn't, supplementation won't help and carries risks.

Frequently Asked Questions

Can I get too much iron from food alone?

No. Your body absorbs only what it needs from food, and excess iron is not absorbed. Iron overload happens only through supplements, fortified foods eaten in very large quantities, or genetic conditions like hemochromatosis. This is why iron supplements carry a risk that food does not.

Does cooking in cast iron increase the iron in food?

Yes, slightly. Acidic foods like tomato sauce leach small amounts of iron from cast iron cookware into the food. The amount varies based on cooking time, acidity, and the age of the pan. It's a minor source compared to iron-rich foods, but it does contribute.

Why does spinach have a reputation for iron but isn't actually a great source?

Spinach contains a lot of iron, but it also contains oxalates, compounds that bind to iron and prevent absorption. Your body absorbs only about 2 percent of the iron in raw spinach. Cooked spinach has slightly better absorption because heat reduces oxalates, but it's still not an efficient source compared to meat or legumes.

Can iron deficiency cause hair loss?

Yes. Iron is necessary for hair growth, and deficiency can push hair follicles into a resting phase, causing increased shedding. Hair loss from iron deficiency is usually reversible once iron levels are restored, though it can take several months to see improvement.

Is it safe to take iron with other supplements?

Iron interferes with absorption of several other minerals and medications. Calcium, zinc, and some antibiotics should be taken at least two hours apart from iron. If you take multiple supplements or medications, ask a pharmacist or doctor about timing to avoid interactions.